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  1. #1
    Senior Member Three Rings
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    compression test all 4 cylinders 120 psi

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    Does the fact that all 4 cylinders have 120 psi of compression point me in the direction as to what the problem is with this head. I'm not sure what condition could create conditions which all 4 cylinders have the same compression. The next test that I'm going to do is a cylinder leak down. Then I would be ready to remove the cylinder head and evaluate its condition.

  2. #2
    Veteran Member Four Rings jpulll's Avatar
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    Jun 19 2014
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    Ohio

    Healthy would be above 170 psi with minor fluctuation between cylinders. Trying adding a little oil into the cylinders and repeat the test to see if the numbers get higher. If they do, I may be mistaken, but I believe that would point to the piston rings not seating correctly.


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  3. #3
    Senior Member Three Rings
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    ok I will add that to the list of tests to do my cylinder leak down test should also help with that. Thanks

  4. #4
    Veteran Member Four Rings Seerlah's Avatar
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    Quote Originally Posted by jpulll View Post
    Healthy would be above 170 psi with minor fluctuation between cylinders. Trying adding a little oil into the cylinders and repeat the test to see if the numbers get higher. If they do, I may be mistaken, but I believe that would point to the piston rings not seating correctly.


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    Not true. 120psi consistent does not constitute an unhealthy engine, just an old one. Higher the Compression the healthier it is, but lower numbers does not mean it is unhealthy. Having inconsistent numbers is what to worry about.
    I hate it when my car acts like a little bitch, treating me like a bitch

  5. #5
    Registered Member Four Rings EuroxS4's Avatar
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    Jan 24 2010
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    2003 Atlas Grey A4 Avant 1.8T 6speed manual quattro,2002 GSXR 600
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    Paramus,NJ USA

    Doesnt mean engine is unhealthy.I could be slightly out of time by a tooth or two.
    VW/Audi Immobilizer removal and immobilizer adapting solutions for any and all VAG Vehicles,Odometer matching, SKC/Pin retrieval services.Located in Northern NJ.For inquries pm for details.

  6. #6
    Veteran Member Four Rings jpulll's Avatar
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    Quote Originally Posted by Seerlah View Post
    Not true. 120psi consistent does not constitute an unhealthy engine, just an old one. Higher the Compression the healthier it is, but lower numbers does not mean it is unhealthy. Having inconsistent numbers is what to worry about.
    Cool, thanks for the info.


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    2003 A4 1.8T 5-spd w/ Motoza 93/E85.

  7. #7
    Senior Member Three Rings
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    Thanks Seerlah it has 134,000 on the clock so it is on the old side, the tb was done last year so I will check the timing, and redo the compression test adding oil to the cylinders.I'm trying to determine by testing what the problem with this engine is. The original problem with the engine is the loss of heat, the rise of coolant level in the expansion tank when the system is depressurized when at operating temperature, and the gurgling or bubbling sound when the cooling system is placed under 25" hg of vacuum. I use a vacuum coolant fill rig to refill and test the integrity of the cooling system. Usually it is obvious when there is a problem the loss of vacuum is immediate. and won't hold vacuum for long. This engine when it is placed under vacuum it takes several minutes for the vacuum to go down by 10 " hg. So somewhere in the system there is an integrity issue allowing exhaust gasses into the cooling system. When the system is under vacuum the gurgling or bubbling sound seems to be coming from the lower right side of the radiator or maybe the turbo if that is possible. Taking my time and trying to make a diagnosis based on testing and understanding what is going with the engine instead of throwing parts at it. Thanks again!

  8. #8
    Veteran Member Four Rings Spike00513's Avatar
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    Mar 05 2013
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    CA

    unrelated: I want to do a compression test on my engine to assess it's level of health.
    I noticed the manual says that it should be done with the fuel injectors unplugged (so they can't spray fuel), and with the throttle open.

    How did you do it?
    I'm wondering how exactly one is supposed to keep the throttle open, so that the engine can suck in air and compress it I assume.
    IDK if the butterfly valve should be held open by hand, or if foot on the gas pedal would electronically send a signal to open it.
    In other words, cranking (for compression test) with foot depressing gas pedal, vs. not.

    It also said the engine must be warm or hot, and IDK if it must be done wet or dry (with some oil)

    Could the piston rings not seat correctly, or be gummed up with carbon or something?
    I also heard that if a car runs rich, that excess fuel can wash the cylinder walls and end up burning out the rings or something. IDK if this is true or not.
    Because when running normally, I assume it's oil on the cylinder walls (below the rings), and not excess unburned fuel.

    IDK how oil is added to the cylinders. If it's a matter of putting a teaspoon or tablespoon of MMO or something (Marvel Mystery Oil), which claims to be thinner than other oils; maybe it could get into the rings better to create a seal?
    I just wonder if it first has to be cranked with the spark plug hole open (no compression test gauge hooked up yet) with a rag held there by hand, after the oil sits to soak a bit, to catch it splashing up and try getting it out.
    To prevent hydrolocking in the future.

    Air is compressible. Fluid is not. The engine is meant to compress air, but not a bunch of oil in the cylinder.

    There are various products on the market that claim to clean ring packs and help them seat better, to restore compression on old engines. IDK if they're snake-oil or not. Never tried it.

    Quote Originally Posted by refueler View Post
    Thanks Seerlah it has 134,000 on the clock so it is on the old side, the tb was done last year so I will check the timing, and redo the compression test adding oil to the cylinders.I'm trying to determine by testing what the problem with this engine is. The original problem with the engine is the loss of heat, the rise of coolant level in the expansion tank when the system is depressurized when at operating temperature, and the gurgling or bubbling sound when the cooling system is placed under 25" hg of vacuum. I use a vacuum coolant fill rig to refill and test the integrity of the cooling system. Usually it is obvious when there is a problem the loss of vacuum is immediate. and won't hold vacuum for long. This engine when it is placed under vacuum it takes several minutes for the vacuum to go down by 10 " hg. So somewhere in the system there is an integrity issue allowing exhaust gasses into the cooling system. When the system is under vacuum the gurgling or bubbling sound seems to be coming from the lower right side of the radiator or maybe the turbo if that is possible. Taking my time and trying to make a diagnosis based on testing and understanding what is going with the engine instead of throwing parts at it. Thanks again!
    Would one issue possibly be a blown head gasket? Would it be worth trying out a Block Tester?

    Quote Originally Posted by EuroxS4 View Post
    Doesnt mean engine is unhealthy.I could be slightly out of time by a tooth or two.
    Is this something VCDS would show in Measuring Blocks or something?

  9. #9
    Veteran Member Four Rings Seerlah's Avatar
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    Quote Originally Posted by Spike00513 View Post
    Is this something VCDS would show in Measuring Blocks or something?
    There is a measuring block (93) that can show intake cam to exhaust cam deviation. Bentley says you want it ideally zero at idle, with +\-6 degree (KW) deviation being the most. I would assume it uses the crank position sensor and cam position sensor for readings (assumption).
    I hate it when my car acts like a little bitch, treating me like a bitch

  10. #10
    Senior Member Three Rings
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    I prove every day that I'm not very smart. I started out ok I pulled the fuel pump fuse #28 I think and immediately went down hill from there. I didn't warm up the engine or have the butterfly valve open during the compression test. I just hope an engine warm up and valve open increases the pressure not decreases it. Oh well I will try to learn from this I'm getting closer to pulling the head.

  11. #11
    Veteran Member Four Rings Seerlah's Avatar
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    Compression test is done with intake air compressing in the cylinder "after" the intake valves. Having the butterfly valve and throttle body open should allow more air intake, which allows for more air to compress. Warm engine means the pistons are expanded and should leave less room for blow by, so also higher compression numbers. This is how I am looking at it, anyways.
    I hate it when my car acts like a little bitch, treating me like a bitch

  12. #12
    Senior Member Three Rings
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    Well I think that I will redo the compression test the proper way before I start tearing into things. Thank you for the right instructions on performing a compression test.

  13. #13
    Senior Member Three Rings
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    This morning when I started to work on the car the coolant level in the expansion tank was almost down to the bottom hose. I was pretty excited I thought that a bubble had worked its way out as there was no coolant on the ground. So I filled the tank up pulled the hard pipe vent plug until coolant issued from the hole and pulled the heater hose back to expose the bleed hole until coolant came out. So I drove around the neighbor hood until I had heat. I kept driving a little further and after each trip return home to check on coolant level and each time it was at the min level. Eventually I went for 45 min drive and kept checking to see if I still had heat. When I returned home the heat was still working and the coolant level in the tank was still at the min level. I 'm thinking this problem is solved I let it set for a couple of hrs. I have to replace the cv axle and lower rear control arm on my 2002 and yes both of my Audi's are down. I got that taken care of and I decided to go for a ride in the Avant. I was gone for over an hr. I stopped filled up with gas so I checked the tank level still at min and I still had heat. I was pretty confident I had this problem solved so much so I put engine cover and air intake plenum back on. I decided to go for ride tonight I hadn't much more than a mile and I was starting to get heat by the time I had gone 2 miles it was blowing cold air. I pulled over popped the hood and the level in the expansion tank was above the max line. I turned around and went back home discouraged. I was beginning to think that I didn't have to pull the head but it looks like now I will be. It looks like it takes a couple of hrs. driving time to accumulate enough exhaust gasses in the cooling system to cause problems with the heat. Every time the coolant level in the expansion tank is above the max line the hard pipe and upper heater hose have air in them and need to be bled. The only solid thing that I have found so far is when I placed the cooling system under a vacuum to refill the system with coolant. I could hear gurgling/bubbling in the turbo area. The thing is the system held vacuum for close to a minute before any noticeable loss of vacuum. What I'm looking for is there a path from the exhaust side to the coolant side of the turbo and can the turbo charger develop enough pressure to inject exhaust gasses into the coolant.



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